A team of researchers, led by Professor Christopher Monroe from Joint Quantum Institute (JQI) at the University of Maryland Physics , has introduced the first fully programmable and reconfigurable quantum computer module in a paper published as the cover article in the August 4 issue of the journal Nature.

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Photo of an ion trap.

The new device, dubbed a module because of its potential to connect with copies of itself is made of five individual ions, charged atoms — trapped in a magnetic field, whose strength is manipulated in such a way that the ions are arranged in a line. A computer program dedicated to solving a particular problem—on five quantum bits, or qubits—the fundamental unit of information in a quantum computer. Quantum computers promise speedy solutions to some difficult problems, but building large-scale, general-purpose quantum devices is a problem fraught with technical challenges.

“For any computer to be useful, the user should not be required to know what’s inside,” said Monroe, who is also a UMD Distinguished University Professor, the Bice Zorn Professor of Physics, and a fellow of the Joint Quantum Institute and the Joint Center for Quantum Information and Computer Science. “Very few people care what their iPhone is actually doing at the physical level. Our experiment brings high-quality quantum bits up to a higher level of functionality by allowing them to be programmed and reconfigured in software.”

The reconfigurability of the laser beams is a key advantage, Debnath says. “By reducing an algorithm into a series of laser pulses that push on the appropriate ions, we can reconfigure the wiring between these qubits from the outside,” he said. “It becomes a software problem, and no other quantum computing architecture has this flexibility.”

To test the module, the team ran three different quantum algorithms, including a demonstration of a Quantum Fourier Transform (QFT), which finds how often a given mathematical function repeats. It is a key piece in Shor’s quantum factoring algorithm, which would break some of the most widely-used security standards on the internet if run on a big enough quantum computer.

Two of the algorithms ran successfully more than 90 percent of the time, while the QFT topped out at a 70 percent success rate. The team says that this is due to residual errors in the pulse-shaped gates as well as systematic errors that accumulate over the course of the computation, neither of which appear fundamentally insurmountable. They note that the QFT algorithm requires all possible two-qubit gates and should be among the most complicated quantum calculations.

The team believes that eventually more qubits—perhaps as many as 100—could be added to their quantum computer module. It is also possible to link separate modules together, either by physically moving the ions or by using photons to carry information between them.

(via Science Daily, IBT)